A number of seed sensors for use in field seed planting apparatus are known in the prior art. Briefly, these sensors fall into two major categories: mechanical and photo-sensitive type sensors. The former, mechanical sensors generally utilize a highly sensitive mechanical switch interposed in a conduit in the path of travel of seeds being dispensed by the planter, so as to the "tripped" by each seed passing through this conduit. The latter, photo-sensitive type sensors generally include a light source photo-sensitive element mounted generally in facing, opposed relation in the seed conduit, such that passage of a seed through the conduit interrupts the light beam falling from the photo-sensitive element, with a corresponding pulse output.
While the sensors, and particularly the latter type have proven useful and highly reliable in operation, certain problems have nonetheless been encountered in their use. One such problem is the accumulation of dirt, dust and the like within the conduits and in particular around the mechanical switch elements or photo-sensitive elements of the sensors. In the former case the moving part of the switch element may tend to become dirt-encrusted, corroded, or otherwise disturbed, such that their performance suffers. In the case of the photo-sensitive elements, obscuring of the light source or of the photo-sensitive element or both results in a loss of sensitivity in the system, and in extreme cases failure thereof. Moreover, insecticide substances commonly used to coat corn seeds or the like, often be deposited on the inside walls of the conduit, thus further obscuring the surfaces of both light source and photo-sensitive detector.
Modern field planters commonly plant from twelve to as many as twenty-four rows of seeds simultaneously. Accordingly, if all planting chutes are to be monitored, one sensor must be provided for each. The provision of such a large number of sensors has heretofore required considerable redundancy in the circuitry associated with the sensors, if it is desired to simultaneously monitor the passage of seeds through all of the seed chutes whose associated rows are being planted. This is generally been true since the response time of either the mechanical or photo-sensitive elements is generally not rapid enough to permit multiplex scanning at a high enough rate to assure substantially continuous monitoring of all sensors.
Advantageously, microwave sensor in accordance with the present invention provides solutions to both of these problems. Specifically, the effect of dirt, dust or insecticide coating is considerably less significant in a microwave system because the wave length of the radiation is many orders of magnitude greater than that of visable light, whose wave length corresponds roughly to the size of particles of dirt, dust or insecticide, which thereby tend to produce scattering or confusion of visable light. This effect is much less pronounced with microwave radiation. Moreover, microwave video detectors are capable of a response time up to four orders of magnitude greater than that of presently available photo-sensitive devices. As an additional element, a microwave apparatus requires but a single cable be feed to the sensor, as the sensing is based upon a field disturbance by the passage of the seed which is passed back through the same transmission line used to bring the microwave signal into the seed conduit for sensing the seed. In contrast, a photo sensor system requires two cables, one for the light or illumination source and another for the photo-sensitive detector element.
Other objects, advantages and features of the invention will become apparent from the following detailed description of the illustrated embodiment, taken in connection with the accompanying drawings.